The present invention relates to phase-pure lithium aluminium titanium phosphate, a method for its production, its use, as well as a secondary lithium ion battery containing the phase-pure lithium aluminium titanium phosphate.
Recently, battery-powered motor vehicles have increasingly become the focal point of research and development because of the increasing lack of fossil raw materials in the near future.
In particular lithium ion accumulators (also called secondary lithium ion batteries) proved to be the most promising battery models for such applications.
These so-called “lithium ion batteries” are also widely used in fields such as power tools, computers, mobile telephones etc. In particular the cathodes and electrolytes, but also the anodes, consist of lithium-containing materials.
LiMn2O4 and LiCoO2 for example have been used for some time as cathode materials. Recently, in particular since the work of Goodenough et al, (U.S. Pat. No. 5,910,382), also doped or non-doped mixed lithium transition metal phosphates, in particular LiFePO4.
Normally, for example graphite or also, as already mentioned above, lithium compounds such as lithium titanates are used as anode materials in particular for large-capacity batteries.
By lithium titanates are meant here the doped or non-doped lithium titanium spinels of the Li1+xTi2−xO4 type with 0≦x≦⅓ of the space group Fd3m and all mixed titanium oxides of the generic formula LixTiyO(0≦x,y≦1).
Normally, lithium salts or their solutions are used for the electrolyte in such lithium ion accumulators.
Ceramic separators such as Separion® commercially available in the meantime for example from Evonik Degussa (DE 196 53 484 A1) have also been proposed. However, Separion contains, not a solid-state electrolyte, but ceramic fillers such as nanoscale Al2O3 and SiO2.
Lithium titanium phosphates have for some time been mentioned as solid electrolytes (JP A 1990 2-225310). Lithium titanium phosphates have, depending on the structure and doping, an increased lithium ion conductivity and a low electrical conductivity, which, also in addition to their hardness, makes them very suitable as solid electrolytes in secondary lithium ion batteries.
Aono et al. have described the ionic (lithium) conductivity of doped and non-doped lithium titanium phosphates (J. Electrochem. Soc., Vol. 137, No. 4, 1990, pp. 1023-1027, J. Electrochem. Soc., Vol. 136, No. 2, 1989, pp. 590-591).
Systems doped with aluminium, scandium, yttrium and lanthanum in particular were examined. It was found that in particular doping with aluminium delivers good results because, depending on the degree of doping, aluminium brings about the highest lithium ion conductivity compared with other doping metals and, because of its cation radius (smaller than Ti4+) in the crystal, it can well take the spaces occupied by the titanium.
Kosova et al. in Chemistry for Sustainable Development 13 (2005) 253-260 propose suitable doped lithium titanium phosphates as cathodes, anodes and electrolytes for rechargeable lithium ion batteries.
Li1.3Al0.3Ti1.7(PO4) was proposed in EP 1 570 113 B1 as ceramic filler in an “active” separator film which has additional lithium ion conductivity for electrochemical components.
Likewise, further doped lithium titanium phosphates, in particular doped with iron, aluminium and rare earths, were described in U.S. Pat. No. 4,985,317.
However, very expensive production by means of solid-state synthesis starting from solid phosphates, in which the obtained lithium titanium phosphate is normally contaminated by further foreign phases such as for example AlPO4 or TiP2O7, is common to all of the above-named lithium titanium phosphates. Phase-pure lithium titanium phosphate or phase-pure doped lithium titanium phosphate has been unknown thus far.